Magnetron



Oct. 21, 1947. Q OKRESS 2,429,291

MAGNETRON Filed July 1, 1943 2 Sheets-Sheet l INVENTOR E. c. o/rzfssATTORNEY Patented Oct. 21, 1947 MAGNETRON Ernest C. ()kress, Montclair,N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Application July 1, 1943, Serial No.492,995

. 11 Claims. (01. 315-) This invention relates to magnetrons andparticularly to such devices in the ultra high frequency or so-calledmicro-wave range which, though not definitely defined, may be consideredas certainly including wave-lengths up to one hundred centimeters.

Magnetrons as heretofore constructed have had a generally symmetricalarrangement of cavities, of which examples may be seen in my priorapplication, Serial No. 460,376, filed October 1, 1942, entitledMagnetron and method of manufacture, and assigned to the same assigneeas the present application. The prior art, in its relation to theinvention here disclosed, may be summarized as providing generallycylindrical central cavity for the cathode, and having a plurality ofradiating cavities evenly spaced around and opening into the centralcavity. An even number of radiating cavities constitute the multiplicitythereof used, and in quantity usually range from six to ten with eightradiating cavities most commonly employed. This prior art type ofmagnetron has serious disadvantages amongst. which may be mentioned thedifficulty in fabrication of obtaining the requisite accuracy which hasto be in some instances within 10.0005 of an inch. Manufacture isconsequently expensive and involves many discarded magnetrons due todiscrepancy from the permitted tolerance. It has also been found thatthe muJti-cavity magnetrons of the prior art promote oscillation orresonance in a plurality of modes rather than just a desired singlemode. Strapping of alternate anode segments has been resorted to in theprior art in an eifort to overcome this undesirable behavior, but notwith complete success, and in addition added electrical and mechanicaldifficulties are introduced,

The present invention has for it general object the purpose ofpresenting another means whereby such difliculties and deficienciesencountered in prior art magnetrons may be alleviated.

More specifically, an object of the invention is to overcomeconstruction and operation productive of undesired modes of oscillation.

Another object of the invention is to simplify construction both tolessen the difilculty of satisfactory manufacture and cost and to reducepercentage of discards.

A further object of the invention is to enable th size of the magnetronfor a given wave-length to be less than heretofore.

Again, an object of the invention is to provide a construction admittingof less critical tolerances without materially afiecting operation.

Still further objects will appear as the description proceeds, both bydirect recitation thereof and by implication from the context.

Referring to the accompanying drawing in which like numerals ofreference indicate similar parts throughout the several views;

Figure 1 is a cross-sectional view, normal to the axes of the severalcavities, of a magnetron constructed in accordance with my invention, asupon line II of Fig. 2; I

Figure 2 is a vertical section on a plane defined by the axes of thecathode cavity and of the input and output leads;

Figure 3 is a sectional view as on arcuate line III-III of Fig. 1 forpurposes of showing graphically the magnetic field lines of force in theresonant cavities;

Figure 4 is a diagrammatic view similar in nature to Fig. 1 butgraphically showing the E and H lines theoretically present in thecavities;

Figure 5 is a vertical sectional view similar to Fig. 2 and showing aconstruction modified as to output lead, the section being taken on aplane indicated by line VV of Fig. 6;

Figure 6 is a cross-sectional view on line VI-VI ing to Fig. 8 butmodified as to character of cavity resonators and output coupling.

In the specific embodiment of the invention illustrated in said drawingand directing attention particularly to Figures 1 to 6 thereof, thereference numeral 15 designates a cylindrical magnetron body having endplates or covers 10 sealed thereto whereby the interior may beevacuated. The interior of said body is formed to comprise an anode llof generally cylindrical shape, shorter than the body which has endflanges l8 for spacing the covers I6 from the ends of the anode andthereby afford the usual and necessary end spaces I9 within themagnetron.

The present showing of the magnetron preferably provides a cathodecavity 20 parallel to but offset from or eccentric with respect to theaxis of the anode body and magnetron, said cavity extending through theanode so as to open into Likewise eccentric to the;

both end spaces l9.

3 anode axis and extending longitudinally through the anode to the endspaces l9 are a plurality of resonant cavities 2| which are otherwiseseparate from each other but open longitudinally at the side of thecathode cavity as by constriction 22 and constitute cavity resonators.In Figures 1 to 6, two cavity resonators 2i are shown of. generallycylindrical shape andwith distinct slot-- like constrictions 22interposed between the cylindrical part of the cavities 2| and theoathode cavity 20. In Figure '7, two cavity resonators Zla are shown ofslot-like formation and in continuation of the slot-like constrictions22a, to

the cylindrical cathode cavity 20a and allwithin.

an anode I la of a magnetron otherwise substantially as described above.These two exemplifications illustrate the feature of eccentricityof.cathode cavities in an anode and with two cavity-res scribed-above.And, furthermore, the feature of eccentricity with a plurality, morethan two, of slot-like cavity resonators maybe employed and isexemplified in Figure 10, wherein threeslotlike resonant cavities 210are shown, the side walls of which are in continuation of the slot-likeconstrictions 220 to the cylindrical cathode cav= ity 200 showneccentrically situated in an anode llc of a magnetron otherwisesubstantially as described above.

Consequently, in all forms of the invention shown, the cathodecavi-ty'iseccentric to and at one-side'of the axis of the anode body and thecavityresonators are at'an opposite side of the axis and a'constrictionlengthwise of the cavities connects each cavity resonatorwith'thecathodecavity. Also in all forms of the invention, the ends ofall cavities open into end spacesin the magnetron 4 body,

Otherstructurescommon to all forms of-the invention, and accordinglyidentified throughoutbythe same reference numerals, comprises a cathode23 extending through the cathode cavitycoaxial therewith and into theend spaces of the illustrated magnetron. The cathode is supported at itsends by ceramic or other insulating collars 24 011- the outer ends ofwhich are mounted metal discs 25 to which lead-in wires 2&arerad-iallyattached. These lead-in wires are sealed through appropriate sealingmeans 21 for the purpose at the side of the magnetron. A heater filament28 extends through the cathode and is attached at its ends to said discs25.

An output connectionis made appropriately from within the magnetron.--

spacewith-symmetrical disposition of the cavity resonators onoppositesides of the output. this-instance, as shown in Figures 1 and 2,the

output 29 is a wire, the end of which is embedded inthe partitionbetween two cavity resonators andnextthe cathode-cavity, said wire-atits embedded end portion being parallel to the axis of the cathodecavity and projecting away from the. end oi the anodeinto. theendj'space where. it'. bends at right angles and extends through the endIn constructions having an even number ofcavi-tyresonators, theoutputmay conveniently be situated inan-en-d- "in a middle one of theseveral cavities.

the three cavities.

= radius particularly by reducing thelatter:

space medially across said partition and out through the side wall ofthe magnetron through appropriate sealing means 30. It is, however,within the scope of the invention to otherwise situate and construct theoutput lead. For instance, as shown in Figures 5 and 6, the output lead3] is introduced midway of the length of one cavity resonator 2i and inthe form of a loop, the plane of which is transverse to the caviti axis.With use of an odd number of cavity resonators, it is convenient tosituate the output lead For instance, in the showing of Figures 8 and 9,there are three cylindrical cavity resonators, and a looped output lead3| as above described may also be used here and inserted in the middleone of In Figure 10 showing three slot-type cavity resonators, theoutput 32 may conveniently have the form of a probe entering the middleone of said slot cavities perpendicular thereto.

With magnetrons as here, disclosed in which more than two cavityresonators are employed, it is preferable'to strap alternate partitionsto each other, and by way of illustration staple-like straps 33 made ofwire are shown in Figures 8 and 9.

The field conditions existing in the cavity resonators are indicated inFig. 4 wherein are shown E lines representative of the electriccomponent of the electromagnetic field and circles representative of theH or magnetic component ofthe electromagnetic field. The direction ofthe flux-lines H isindicatedby theusual dot'and cross within thecircles, the dot indicating direction toward the reader and the crossindicating direction-away from the reader. Conduction and displacementcurrents'fiow in accordance with Maxwellstheory, for theboundary'conditions imposed as indicated'in Figure 4;

Field'conditionsin the solid angle, 0: (see Fig. 4) are similar to thoseexisting'in the symmetric form.- The 'D. C. fields required are higher,espe ially the cut-01f voltage. Both may be compensated byaltering1both' the cathode and anode The dimensions of the resonatorsystem do not materiallydepart from'the relations for themultiple cavitymagnetron.

The dual cavity deviceoperateson thebu-nchercatcher principle. Externalcoupling should'be madein the cavity which acts asacatcher as determinedby the axial magnetic field-polarity; A three-cavitysystem shouldoperate equally well witheitherdirection of theaxial magnetic field"with the coupling device in the cavity as shown in Figure 8.; Crossstrapping as shown in thisfigurewill improve the efficiency of operationin the fundamental. .mode.

It isa factthata magnetron-constructed in accordance with the presentinvention-utilizing eccentric disposition of cavities and limited numberof resonant cavities may be made much smaller than, the prior artconventional symmetrical magnetron. The" reduced number of cavitiesalso" reduces manufacturing operationsand cost, and it hasbeenadvantageously ascertained that tolerances of dimensions are less.

1. A magnetronhavingan,anode. bodysub v stantially cylindrical about anaxis, said body having cavities therein longitudinally parallel to eachother and to said axis, said body completely surrounding said cavities,one cavity of said cavities being axially ofiset from the said axis ofthe body and all other of said cavities radiating from the said onecavity, and a cathode in said one cavity.

2. A magnetron having an anode body substantially cylindrical about anaxis, said body having cavities therein longitudinally parallel to eachother and to said axis, said body completely surrounding said cavities,one of said cavities being cylindrical and axially offset from the saidaxis of the body and constituting a cathode cavity, and all other ofsaid cavities each radiating from the said cathode cavity, and a cathodein said one cavity.

3. A magnetron having an anode body substantially cylindrical about anaxis, said body having cavities therein longitudinally parallel to eachother and to said axis, said body completely surrounding said cavities,one of said cavities being cylindrical and axially ofiset from the saidaxis of the body and constituting a cathode cavity and all other of saidcavities constituting cavity resonators and each radiating from the saidcathode cavity and having a width perpendicular to direction ofradiation less than the diameter of said cathode cavity, and a cathodein said cathode cavity. A

4. A magnetron having an anode body with a cathode cavity eccentricallydisposed therein on one side of the middle of said body, and with cavityresonators eccentric to the anode body on an opposite side of the middlethereof and radiating from the cathode cavity, and a cathode in saidcathode cavity.

5. A magnetron having an anode body with a cathode cavity eccentricallydisposed therein on one side of the middle of said body, and dual cavityresonators eccentric to the anode body and both on an opposite side ofthe middle thereof and radiating from the cathode cavity, and a cathodein said cathode cavity.

6. A magnetron having an anode body with a cathode cavity eccentricallydisposed therein on one side of the middle of said body, and more thantwo cavity resonators eccentric to the anode body, all of said cavityresonators being on an opposite side of the middle of the anode body andradiating from the cathode cavity, and a cathode in said cathode cavity.

'7. A magnetron having an anode body with a cathode cavity eccentricallydisposed therein on one side of the middle of said body, and an oddnumber more than two of cavity resonators eccentric to the anode body,all of said cavity resonators being on an opposite side of the middle ofthe anode body and radiating from the cathode cavity, and a cathode insaid cathode cavity.

3. A magnetron having an anode body with a cathode cavity eccentricallydisposed therein and with an odd number only of evenly-spaced cavityresonators radiating from thereby providing one radiating cavityresonator symmetrically between other radiating cavity resonators, andan output lead partially in and extending from said one radiating cavityresonator symmetrically between other radiating cavity resonators.

9. A magnetron having an anode body with a cathode cavity eccentricallydisposed therein entirely on one side of the middle of said body, andsaid body having only two cavity resonators of diverging slot formationradiating from said cathode cavity on an opposite side of the middle ofsaid body.

10. A magnetron having an anode body with a cathode cavity eccentricallydisposed therein entirely on one side of the middle of said body, saidbody having an odd number only of cylindrical cavity resonators on theopposite side of the middle of said body from the said cathode cavity,

and said cylindrical cavity resonators each having a slot connectionwith the cathode cavity.

11. A magnetron having an anode body with a cathode cavity eccentricallydisposed therein entirely on one side of the middle of said body, saidbody having a total of only three slotlike cavity resonators radiatingfrom said cathode cavity, and a probe-like output lead partially withinand protruding laterally from the middle one of said cavity resonators.

ERNEST C. OKRESS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,410,396 Spencer Oct. 29, 19462,408,237 Spencer Sept. 24, 1946 2,406,277 Bondley Aug. 20, 19462,408,234 Spencer Sept. 24, 1946 2,084,867 Prinz et a1 June 22, 19372,348,986 Linder May 16, 1944 2,075,855 Kilgore Apr. 16, 1937 2,071,311Linder Feb. 16, 1937 2,115,521 Fritz et al Apr. 26, 1938 2,167,201Dallenbach July 25, 1939 2,063,342 Samuel Dec. 8, 1936 FOREIGN PATENTSNumber Country Date 215,600 Switzerland Oct. 16, 1941

